1. THE UNIVERSE
Part 1: stars

2. Stars What is the universe?
The universe is the name given to everything that exists, all space and time. This includes moons, planets, stars, galaxies. There is an awful lot of “stuff” that makes up the universe.

3. Stars

4. Stars
Gravity

5. Stars
What are Stars?
Stars are gaseous objects that give off light and heat…

6. Stars
As the distance between stars is so large, it is often described in light years. One light year is the distance that light travels in one year. This distance is 9.5  1012 km or 9.5  1015 m.
Another commonly used method of measuring astronomical length is the parsec
1 parsec = 3.26 light years
𝐷𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑖𝑛 𝑝𝑎𝑟𝑠𝑒𝑐𝑠= 𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒 𝑖𝑛 𝑙𝑖𝑔ℎ𝑡 𝑦𝑒𝑎𝑟𝑠 3.26

7. Stars
Question How far away, in parsecs, is Earth from Alpha Centauri, knowing that it is 4.22 Light Years away?

8. Stars
Astronomers refer to the brightness of a star as its magnitude. A star's apparent magnitude is a measure of the brightness of a star as it appears to an observer on Earth. The colour of a star is due to its temperature.
Note that the brightest stars have the lowest magnitudes, which may even take on a negative number

9. Stars
A more accurate indication of the brightness of a star is the absolute magnitude. This is the measure of brightness if all stars were all 10 parsecs from Earth.

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Which of these stars do you think is the brightest based on their Apparent Magnitudes? Can you tell which star is the closest?
Sirius- -1.5
Bellatrix- 1.6
Alpha Centauri- -0.3

12. Stars
Parallax
Stars change their position in the sky depending on the position the Earth is in its orbit.

13. Stars
Parallax Activity

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With our eyes we can see only a very small range of wavelengths of light.
Others that we cannot see include X-Rays, microwaves, radio and TV, Ultraviolet, etc.
Because light is based on electrical and magnetic effects it can be placed on a scale called the electromagnetic spectrum.

15. Stars
Astronomers can analyse the light from a star to determine its colour or spectral type. The colour of a star corresponds to its temperature. Blue stars are the hottest (about 20,500C), whereas red stars are the coolest (less than 3000C).

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Nuclear Fusion
The energy supply for stars including our Sun is a nuclear reaction called nuclear fusion. Nuclear reactions involve changes to the particles in the nucleus and produce huge amounts of energy.
This reaction involves the splitting up of atoms into its components. These free flowing electrons and protons form plasma
A common example of plasma is lightning

18. Stars
In the core of stars, hydrogen nuclei join together to produce helium, and in the process they release enormous amounts of energy. This reaction is called nuclear fusion
The huge gravitational force brings them close enough to collide and they can bond together and form new isotopes and elements.

19. Stars
Overall hydrogen is converted into helium, producing huge amounts of energy, in the process of nuclear fusion.
Stars with higher gravitation and temperature are able to fuse hydrogen and helium into even larger nuclei such as beryllium, carbon, oxygen, … etc.

20. Stars
Recall that Suns are undergoing a constant internal battle Gravity is pulling in Radiation Pressure from the fusion reaction is pushing out These two factors determine the life of a star

21. Stars Life Cycle of Stars
Hertzsprung-Russell Diagrams provide a way of classifying stars. They act as diagrams for mapping out the life cycle of stars. The diagram shows a relationship between a stars brightness and temperature

22. Stars Life Cycle of Stars
The majority of stars fall under a grouping called the main sequence. These stars have a balance of Gravitational force and Radiation pressure, making them relatively stable.

23. Stars Life Cycle of Stars
Red Giants are average sized stars that are beginning to run out of hydrogen in their core, so begin to burn the hydrogen in their outer layers. As a result, they have a small core, with lower temperatures. This results in light being produced at the red end of the spectrum.

24. Stars Life Cycle of Stars
As the helium produced in the outer layers falls into the core, it undergoes fusion and collapses the star further. The outer layers begin to escape, spreading out as a gas cloud called a Nebula. The leftover core is densely packed and has a high temperature and is known as a White Dwarf

25. Stars Life Cycle of Stars
Supergiant's are massive stars, ten or more times the size of our sun. As seen on the H-R diagram below, they lie across the top You can see how they move horizontally, rather than diagonally

26. Stars Life Cycle of Stars
Supergiant's use up all their hydrogen quickly, causing helium to fuse in the core. Their brightness stays about the same, but the temperature decreases. They will continue to fuse heavier atoms until they run out of fuel, causing a supernova.

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Supernova
Once atoms have fused to the point of producing Iron, the fusion process stops. As the core has stopped producing energy, the force of gravity outweighs the radiation pressure causing rapid collapse with massive force. The rebounding explosion is called a supernova.

28. Stars
After a Supernova, the forces of gravity cause atoms to break down. Electrons and Protons combine to form Neutrons, resulting in what is known as a dense neutron star. Imagine trying to make a snowball by compacting as much ice as possible…

29. Stars Finally…… A Black Hole
The remnants of a supernova have such a massive gravitational force that its mass collapses further into an object called a singularity, or as it is more commonly known- black hole.

30. Stars
The forces of gravity are so massive, not even light can escape. This is why they cannot be ‘seen’, but appear as black. The force of this gravitational pull can be seen when it exists in a binary system. Material from one star can be ripped out ‘consumed’ by the black hole